Field of the Invention
The present invention relates to power modules including packages.
Description of the Background Art
Proposed are various techniques concerning power modules capable of switching a large current quickly. One example of such techniques includes a power module including an embedded capacitor, as proposed in Japanese Patent Application Laid-Open No. 2009-225612. In such a configuration, a snubber capacitor for reducing or eliminating surge voltage is connected to be adjacent to semiconductor switching elements (upper arms and lower arms) of individual sets. This enables the surge voltage to be reduced properly.
However, since the surge voltage varies depending on conditions of user's use of the module, the capacitance of the snubber capacitor needs to be optimized for each of the conditions of user's use in order to sufficiently reduce the surge voltage. Further, since capacitors are likely to have varied capacitances depending on a temperature change, the capacitor within the module is likely to have varied capacitances under the influence of heat generation of chips. This is particularly seen in a capacitor that uses a material having a high dielectric-constant (high dielectric) because the capacitance of such a capacitor is greatly subject to change depending on the temperature change. Thus, the capacitor cannot continue to have an appropriate capacitance enough to reduce the surge voltage. Unfortunately, this can cause the surge voltage to increase to the extent that the surge voltage exceeds element breakdown voltage.
To solve this problem, a capacitor having a large capacitance may be embedded in the module beforehand in light of the variations in capacitance of the capacitor. In such a case, however, a larger space than is required needs to be allocated within the module. This additionally results in a higher cost than is required and a larger apparatus than is required.
Furthermore, the high dielectric used for the capacitor is a sintered body; and it is difficult to sinter the dielectric of the capacitor together with a lead at high temperature. Hence, it is not possible to use a snubber capacitor having an appropriate capacitance enough to reduce the surge voltage. Unfortunately, this possibly causes the surge voltage to exceed the element breakdown voltage.